Telecommunications – Carrier wave repeater or relay system – Plural modulated carriers
Patent
1997-06-25
1999-10-05
Le, Thanh Cong
Telecommunications
Carrier wave repeater or relay system
Plural modulated carriers
455 21, 455 24, H04B 714
Patent
active
059638478
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a booster system that is used to improve the reception in areas of weak radio waves, in a mobile communication system such as a radio paging system, in particular.
In mobile communication systems, communication quality declines in areas where radio waves from the base station are weak, for example, around zone edges (cell edges). Furthermore, since radio waves from the base station do not reach the back of a mountain, there are areas where no services can be provided because of some particular geographical features. Even in such areas high quality services could be offered by increasing the number of base stations, but this inevitably leads to the defect of increased costs for services.
As a solution to this problem there has been used a booster system capable of easily relaying radio waves. The booster system receives a desired signal, then amplifies the received signal, and sends radio waves of high intensity toward an object area at the same frequency as that of the received signal. However, the booster system has to clear some conditions. One of the most important issues is mutual coupling between a transmitting and a receiving antenna, resulting in amplified radio waves of high intensity, emitted from the transmitting antenna, getting mixed into signals received originally by the receiving antenna. The interference waves thus mixed in the received signals act as interference waves and make the booster operation unstable. As a solution to this problem, it is customary to space the two antennas sufficiently far apart so as to loosen the mutual coupling between them. In recent years, however, there is a need of downsizing the whole apparatus to reduce the cost for installation of the booster system--this makes it difficult to reduce the mutual coupling between the transmitting and receiving antennas by spatially separating them.
To meet the requirement, there have been proposed methods wherein the booster system is equipped with an interference canceling function as described below.
A first method is to superimpose a pilot signal on the send signal. With this method, as shown in FIG. 1, a received signal, which is the input into a receiving antenna 11, is combined by a combiner 12 with a feedback signal, then the combined signal from the combiner 12 is subjected to processing for the removal of out-band signals by band-pass filters 13 and 14 properly amplified by an amplifier 15, then the amplified signal is combined by a combiner 17 with a pilot signal from a pilot signal generator 16, and the combined signal is sent as the send signal via a transmitting antenna 18. On the other hand, the output send signal from the combiner 17 is branched by a coupler 19 and the branched signal is adjusted by an amplitude/phase controller 21 in amplitude and in phase, thereafter being fed as a feedback signal to the combiner 12. The combined signal from the combiner 12 is branched by a coupler 22, then a pilot signal is extracted by a filter 23 from the branched output, then the extracted signal and the pilot signal from the generator 16 are compared by a comparator 24, and the amplitude and phase of the feedback signal are controlled by the amplitude/phase controller 21 with the output from the comparator 24 so that the pilot signal component is reduced to zero in the combined signal from the combiner 12.
This method has a shortcoming that the send signal is disturbed by the addition thereto of the pilot signal.
A second method is to amplify the received signal after modulating it by a modulating signal. According to this method, as shown in FIG. 2, the combined signal from the combiner 12 is branched by the coupler 22 and is then demodulated by a demodulator 26 to obtain a modulated signal component, which is correlated by a correlator 28 with a modulating signal from a modulating signal generator 27, and the amplitude/phase controller 21 is controlled so that the correlation becomes zero. After having its out-band component rejected by the band-pass filter 13, the co
REFERENCES:
patent: 4317217 (1982-02-01), Davidson et al.
patent: 4776032 (1988-10-01), Odate et al.
Ebine Yoshio
Ito Kazuhito
Nakada Manabu
Suzuki Hiroshi
Cong Le Thanh
NTT Mobile Communications Network Inc.
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